Portable systems, such as portable computers, have become increasingly popular as replacements for desktop systems. A portable system relies on a battery as its power source when it is not connected to an external power source, such as an AC outlet. As battery life is limited, power consumption in the system is reduced typically by lowering the core supply voltage and the core clock frequency of the processor. Thus, the portable system operates in a high performance state when it is powered by an external source and in a low power state when powered by a battery.
In some portable systems, the transition between the two states occurs statically, for example, at reset or reboot. The state transition processor technology, on the other hand, is capable of dynamically transitioning between the two states, i.e., without a processor reset. The technology is an improvement over the technology that changes the performance states statically because it achieves the transitions seamlessly and relatively rapidly without user intervention.
Even this technology, however, may take more than 500 micro seconds to adjust the core supply voltage and the core clock frequency of the processor. This latency is the result of the processor being placed in the deep sleep mode (ACPI Specification C3 mode) during the entire transition. ACPI Specification stands for the Advanced Configuration and Power Interface Specification, Revision 2.0, published on Jul. 27, 2000. Additional latency results to re-activate the system clock input to the processor to enable it to exit deep sleep following the transition.
The high processor latency typically associated with transitioning states is undesirable because it is wasted time that slows down the system operation.